Biofuel production by high temperature non-faradaic electrochemical modification of catalysis

ABSTRACT

A method for producing biofuels from biomass in which a refined biomass material is introduced into a non-Faradaic electrochemical device, preferably at a temperature greater than or equal to about 150° C., and deoxygenated and/or decarboxylated in said device to produce an increased carbon chain fuel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for producing biofuels. In oneaspect, this invention relates to a method for producing biofuels frombiomass. In another aspect, this invention relates to the production ofbiofuels using the NEMCA effect, i.e. non-Faradaic electrochemicalmodification of catalytic activity, also known as electrochemicalpromotion of catalysis (EPOC).

2. Description of Related Art

The principal methods for producing chemicals from biomass are biomassrefining or pretreatment, thermo-chemical conversion (gasification,pyrolysis, hydro-thermal-upgrading (HTU)), fermentation andbioconversion, and product separation and upgrading. There are five maincategories of building blocks that can be identified as intermediatesfor the production of chemical products from biomass:

-   -   1) Refined biomass, i.e. biomass from which the valuable        components, having been made accessible by physical and/or mild        thermo-chemical treatment, are extracted after which the        remaining biomass undergoes further transformation;    -   2) Biosyngas, primarily CO and H₂, which is a multifunctional        intermediate for the production of materials, chemicals,        transportation fuels, power and/or heat from biomass and which        can easily be used in existing industrial infrastructures as a        substitute for conventional fossil-based fuels and raw        materials;    -   3) Mixed sugars, C₅ and C₆ sugars, which are further refined        substrates for chemical and bioconversion and which mainly        originate from side streams in the food industry and potentially        from ligno-cellulosic biomass streams;    -   4) Pyrolysis oil, i.e. oil produced in fast and flash pyrolysis        processes which can be used for indirect co-firing for power        production in conventional power plants, for direct decentral        heating purposes, and potentially as high energy density        (important in case of long distance transportation) bio-based        intermediates for the final production of chemicals and/or        transportation fuels; and    -   5) Biocrude, i.e. fossil oil-like mixture of hydrocarbons with        low oxygen content, which results from severe        hydro-thermal-upgrading of relatively wet biomass and which        potentially can, like its petroleum analog, be used for the        production of materials, chemicals, transportation fuels, power,        and/or heat.

Refined biomass comprises primarily mixed sugars, fatty acids, orsyngas. The transformation of refined biomass into a variety of chemicalproducts, such as fuels, is a very complicated process due to theimportance of separation technology in providing an efficient and costeffective biocatalytic production process. Different refined biomassesrequire different treatments to become useful products. For example,fatty oil is processed through a transesterification reaction to produceuseful biodiesel fuel. In this case, KOH is used as a catalyst whilefats and oil react with methanol. However, the complicated processinvolves complicated separation paths and is apparently neithereffective nor efficient.

The NEMCA effect is based on the discovery that by applying an electricvoltage between, on the one hand, an active material which is applied,preferably in the form of layers, to a solid electrolyte and, on theother hand, a further metallic substrate, also preferably in the form oflayers, which is in turn connected to the solid electrolyte, it ispossible for the activity or selectivity of a catalyst to be greatlyaltered. More particularly, it has been found that when using an O²⁻,H⁻, or other ion conducting solid electrolyte in a catalyticelectrochemical device, the catalytic reaction rate is significantlygreater (on the order of 10⁵ times greater) than the Faradaic rate.These phenomena have been observed, for example, in the hydrogenation ofunsaturated organic compounds. See U.S. Pat. No. 6,194,623, whichteaches a process for the selective hydrogenation of at least oneorganic compound having at least one unsaturated group, using the NEMCAeffect, wherein the at least one organic compound having at least oneunsaturated group is a hydrocarbon having C—C double bonding or at leastone C—C triple bond, or a mixture of at least one hydrocarbon having atleast one C—C double bond and at least one hydrocarbon having at leastone C—C triple bond. The at least one organic compound is brought intocontact with a hydrogen-containing gas in the presence of a catalyst,wherein the catalyst comprises an active material which is applied to asolid electrolyte to which, in turn, a metallic substrate is connectedin such a way that a current flows through the solid electrolyte, sothat the active material can be kept at a constant potential and avoltage is applied to the catalyst during the hydrogenation. More than70 different catalytic reactions (oxidations, hydrogenations,dehydrogenations, isomerizations, decompositions) have beenelectrochemically promoted on Pt, Pd, Rh, Ag, Au, Ni, IrO₂, and RuO₂catalysts. The solid electrolytes are O²⁻ conductors, such as Y₂O₃stabilized ZrO₂ (YSZ), H⁺ conductors, such as CaZr_(0.9)In_(0.1)O_(3-α)and NAFION®, F⁻ conductor (CaF₂), and the like. However, no incrementalchain increases have been found to occur.

Deoxygenation and decarboxylation are rarely reported at hightemperatures with big molecules, for example, chains with more than fivecarbons. However, in the liquid phase, decarboxylation has beenreported. See, for example, U.S. Pat. No. 6,238,543, which teaches aprocess for electrolytic coupling of carboxylic acids carried out in apolymer electrolyte membrane reactor in which gaseous or neat (i.e.without water) liquid reactants are used without the use of organicco-solvents while preventing the loss of platinum and permitting the useof oxygen reduction to water as the cathode reaction. In this case, theuse of a neat organic acid is necessary to prevent oxygen production atthe anode electrode. Consequently, the method disclosed therein, whichis necessarily carried out at temperatures less than 120° C. due, amongother things, to limitations of the NAFION electrolyte employed thereinand which requires cell potentials of at least about 3.0 volts, cannotbe used for bio-oil treatment due to the presence of about 17% by weightwater therein.

SUMMARY OF THE INVENTION

It is, thus, one object of this invention to provide a high temperatureNEMCA reactor coupling high temperature biomass hydrolysis andhydropyrolysis products to produce high heat value, long C—C chainfuels.

It is another object of this invention to provide a method fordeoxygenation and decarboxylation in which a catalyst is used forpromotion of the deoxygenation and decarboxylation reactions.

It is yet another object of this invention to combine the catalyticdecarboxylation and deoxygenation with electrochemicaloxidation/reduction.

These and other objects of this invention are addressed by a method forproducing biofuels comprising the steps of introducing a refined biomassmaterial comprising water into a non-Faradaic electrochemical device anddeoxygenating and/or decarboxylating the refined biomass material in thedevice, producing an increased carbon chain fuel. In accordance with onepreferred embodiment, the reactions are carried out at a temperaturegreater than or equal to about 150° C. For a refined biomass material inwhich the reactants are an organic acid and alcohol, the reactions areas follows:

At the anode: RCOOH+R′COOH→R—R′+CO₂+2H⁺+2e⁻

At the cathode: ROH+R′OH+2H⁺+2e⁻→R—R′+2H₂O

where R and R′ are preferably selected from the group consisting ofalkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl,substituted alkynyl, phenyl, substituted phenyl, aralkyl,ring-substituted aralkyl, and mixtures thereof. Carbohydrate and fattyacid biomass can be electrochemically treated to become useful fuels atelevated temperatures. The selective oxidation and reduction methodeliminates impurity separations in the process of biofuel productionbecause the R—R′ product is more hydrophobic and easy to separate fromhydrophilic liquid. At the same time, the electrochemically promotedcatalysis increases the biofuel reaction kinetics. Reactor surfacefouling which may occur can be removed by electric shocking.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of this invention will be betterunderstood from the following detailed description taken in conjunctionwith the drawings wherein:

FIG. 1 is a diagram showing the deoxygenation of OH-based refinedbiomass products such as sugar and alcohol to high heat capacity fuel inaccordance with one embodiment of this invention;

FIG. 2 is a diagram showing the decarboxylation of a refined biomassmaterial comprising acid-based biomass products, such as fatty acids, tohigh heat value capacity fuel;

FIG. 3 is a diagram showing a combined deoxygenation and decarboxylationreaction for making high heat value fuel from alcohol and organic acid;and

FIG. 4 is a simplified diagram of a NEMCA reactor in accordance with oneembodiment of this invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS Definitions

As used in the description and claims, the term “increased carbon chainfuel” refers to a fuel in which the carbon chain is incrementally longerthan the carbon chains of the individual reactants.

As used in the description and claims, the term “refined biomassmaterial” refers to carbohydrates, organic acids, and alcohols derivedfrom biomass.

As used in the description and claims, the term “non-Faradaicelectrochemical device” refers to an electrochemical cell comprising aproton conductive membrane disposed between a catalytic anode electrodeand a catalytic cathode electrode in which electricity from an externalsource is provided between the catalytic anode electrode and thecatalytic cathode electrode, resulting in increased catalytic activityor selectivity.

In this invention, non-Faradaic electrochemical modification ofcatalytic activity is used to convert refined biomass materials touseful fuels. In accordance with one embodiment of this invention, ahigh temperature proton conductive membrane is used to transport protonsfrom the anode electrode to the cathode electrode of an electrochemicalcell at a temperature greater than about 150° C., preferably at atemperature in the range of about 150° C. to about 600° C. Operation atthese temperatures enables the use of cell potentials less than or equalto about 2.5 volts, substantially lower than conventional NEMCA systems.Under these conditions, alcohols can be deoxygenated and organic acidscan be decarboxylated. In accordance with one preferred embodiment, asilver-containing catalyst employed in the anode electrode is depositedonto one side or face of a proton conductive membrane and aNiO-containing catalyst employed in the cathode electrode is depositedonto the opposite side or face of the proton conductive membrane.External electricity is added between the anode and cathode electrodesto promote the deoxygenation and decarboxylation reactions. Any externalsource of electricity may be employed. In accordance with one preferredembodiment of this invention, the electricity is generated by arenewable energy source, such as solar energy, wind energy, geothermalenergy, wave energy or tides, and the like. The method of this inventionis particularly suitable for use with such renewable energy sources asit provides a means for storing such energy forms. In addition, thefuels generated by the process may be used to generate electricity,which, in turn, may be introduced into the electrical grid as needed ordesired, such as at times of peak loads.

FIG. 1 shows the reaction diagram in accordance with one embodiment ofthis invention in which the refined biomass material comprises OH(hydroxyl)-based biomass products on the cathode electrode facing sideof the proton conductive membrane and the deoxygenation reaction occursat the cathode electrode. FIG. 2 shows the reaction diagram inaccordance with one embodiment of this invention in which the refinedbiomass material comprises acid-based biomass products disposed on theanode electrode facing side of the proton conductive membrane anddecarboxylation occurs at the anode electrode. FIG. 3 shows the reactiondiagram in accordance with one embodiment of this invention for acombined reactor in which OH-based biomass products are disposed on thecathode electrode facing side of the proton conductive membrane andacid-based biomass products are disposed on the anode electrode facingside of the proton conductive membrane, wherein deoxygenation occurs atthe cathode electrode and decarboxylation occurs at the anode electrode.In accordance with one embodiment of this invention, carbohydrates areprovided to the cathode electrode facing side of the proton exchangemembrane.

FIG. 4 shows a possible reactor design suitable for use in accordancewith one embodiment of this invention. As shown therein, a tubularreactor vessel 10 is used to carry out the reaction. In this reactor,the heated zone 11 is heated for electrochemical reduction/oxidationreactions. Biorefined biomass is introduced into a cool zone at one end12 of the reactor tubes and the products flow out through a cool zone atthe opposite end 13 of the reactor tubes. One of the benefits of thisarrangement is that the end cool zones enable good seals for ceramictubes. The tubes are preferably alumina ceramic tubes embedded withproton conductive ceramic materials, such as rare earth cerate andzirconate perovskites. The ceramic electrolyte that promotes ion andcharge transfer and separates the anode and cathode electrodes, alsoinsulates the anode and cathode electrodes. This creates an electricalpotential between the anode and cathode electrodes. As a result, theelectrons may be released to an external circuit. This direct generationprocess is analogous to the operation of a battery except that thebattery contains all of the necessary reactants internally. Catalystsare deposited on both sides of the alumina tubes and perforated nickeltubes or nickel gauzes are used as current collectors.

Tubular reactors suitable for use in accordance with one embodiment ofthis invention may be prepared using well known tubular solid oxide fuelcell manufacturing methods. The primary difference is the use of protonconductive perovskite oxide materials instead of oxygen ion conductiveceramics. For example, ytterbium doped strontium cerate or yttrium dopedstrontium zirconate materials may be milled with plasticizers, such ascellulose, and solvent, such as xylene, with the resulting mixture beingdried and ground to make a paste for extrusion. After extrusion, theceramic tubes are dried and sintered. Meanwhile, catalyst wet depositionon the anode and cathode electrodes is also performed. Proton conductiveceramics suitable for use in this invention include, but are not limitedto, SrCeO₃, BaCeO₃, CaZr_(0.9)In_(0.1)O_(3-α), and ABO₃ formula oxides,such as LaP₃O₉.

Conway, B. E. et al., “New Approaches to the Study of ElectrochemicalDecarboxylation and the Kolbe Reaction”, Canadian Journal of Chemistry,Vol. 41 (1963), pp. 38-54, teaches that, in an aqueous solution, thedecarboxylation reaction is almost completely inhibited by oxygenevolution in a Faradaic mode of operation. In the invention disclosedherein, the Faradaic reaction is reduced and the non-Faradaic reactionis promoted by using high oxygen evolution overpotential catalysts atthe anode electrode. Electrochemical refining of bio-oil in accordancewith the method of this invention overcomes the problem of oxygenevolution by using highly corrosion resistant bipolar plates, e.g.gold-plated or platinum-plated bipolar plates, with highly protonconductive membranes as well as high oxygen evolution overpotentialcatalysts, such as Ni or Ag deposited on PbO₂, Ni—PbO₂/SnO₂, and othersupport materials having an energy bandgap more than 2.0 eV, includingdiamond powders. For example, Ag—PbO₂/SnO₂ catalyst has an oxygenevolution overpotential at 2.5 V vs. NHE (normal hydrogen electrode)compared with Pt at 1.3 V vs. NHE. Thus, the decarboxylation reaction ismore competitive than oxygen evolution at the anode.

Ag—PbO₂/SnO₂ catalyst maybe synthesized by dissolving 0.3 g AgNO₃ in 50ml of deionized water with 0.74 g PbO₂ and 0.05 g SnO₂, producing acolloid solution, which is then titrated by 0.1 M sodium boron hydride(NaBH₄) to deposit Ag on PbO₂/SnO₂. The resulting solution is thenfiltrated to produce a solid powder, which is thoroughly washed anddried for use in electrode preparation.

While in the foregoing specification this invention has been describedin relation to certain preferred embodiments thereof, and many detailshave been set forth for the purpose of illustration, it will be apparentto those skilled in the art that the invention is susceptible toadditional embodiments and that certain of the details described hereincan be varied considerably without departing from the basic principlesof this invention.

1. A method for producing fuels comprising the steps of: introducingwater and a feedstock material comprising at least one of acarbohydrate, an organic acid, and an alcohol into a non-Faradaicelectrochemical device; and at least one of deoxygenating anddecarboxylating said feedstock material in said device, producing anincreased carbon chain fuel.
 2. The method of claim 1, wherein saiddevice is operating at a temperature greater than or equal to about 150°C.
 3. The method of claim 1, wherein said feedstock material is selectedfrom the group consisting of waste materials, waste water, refinedbiomass materials, waste engine oil, and mixtures thereof.
 4. The methodof claim 1, wherein said feedstock material comprises said organic aciddisposed on an anode electrode facing side of a proton conductivemembrane.
 5. The method of claim 1, wherein said feedstock materialcomprises said alcohol disposed on a cathode electrode facing side of aproton conductive membrane.
 6. The method of claim 4, wherein saidfeedstock material comprises at least one of said carbohydrate and saidalcohol disposed on a cathode electrode facing side of said protonexchange membrane.
 7. The method of claim 1, wherein said non-Faradaicelectrochemical device is operated at an electrical potential of lessthan or equal to about 2.5 volts.
 8. The method of claim 1, wherein saidnon-Faradaic electrochemical device comprises a catalytic anodeelectrode comprising a Ag-containing catalyst.
 9. The method of claim 1,wherein said non-Faradaic electrochemical device comprises a catalyticcathode electrode comprising a Ni-containing catalyst.
 10. The method ofclaim 1, wherein said non-Faradaic electrochemical device comprises aproton conductive membrane comprising a ceramic material.
 11. The methodof claim 1, wherein external electricity is provided to saidnon-Faradaic electrochemical device by a renewable energy source. 12.The method of claim 11, wherein said renewable energy source is selectedfrom the group consisting of solar energy, wind energy, geothermalenergy, wave energy, and combinations thereof.
 13. In an electrochemicaldevice comprising a proton conductive membrane disposed between acatalytic anode electrode and a catalytic cathode electrode and anexternal electricity source providing electricity between said catalyticanode electrode and said catalytic cathode electrode, a method forproducing fuels comprising the steps of: introducing water and afeedstock material comprising at least one of a carbohydrate, an organicacid, and an alcohol into said electrochemical device; and at least oneof deoxygenating and decarboxylating said feedstock material, forming anincreased carbon chain fuel.
 14. The method of claim 13, wherein saidfeedstock material is selected from the group consisting of wastematerials, waste water, refined biomass materials, waste engine oil, andmixtures thereof.
 15. The method of claim 13, wherein saidelectrochemical device is operated at a temperature greater than orequal to about 150° C.
 16. The method of claim 15, wherein saidtemperature is in a range of about 150° C. to about 600° C.
 17. Themethod of claim 13, wherein said electrochemical device is operated atan electrical potential of less than or equal to about 2.5 volts. 18.The method of claim 13, wherein said catalytic anode electrode comprisesa Ag-containing catalyst.
 19. The method of claim 13, wherein saidcatalytic cathode electrode comprises a Ni-containing catalyst.
 20. Themethod of claim 13, wherein said organic acid is disposed on an anodeelectrode facing side of said proton conductive membrane.
 21. The methodof claim 13, wherein said alcohol is disposed on a cathode electrodefacing side of said proton conductive membrane.
 22. The method of claim20, wherein said at least one of said carbohydrate and said alcohol isdisposed on a cathode electrode facing side of said proton exchangemembrane.
 23. The method of claim 13, wherein said external electricityis provided by a renewable energy source.
 24. The method of claim 23,wherein said renewable energy source is selected from the groupconsisting of solar energy, wind energy, geothermal energy, wave energy,and combinations thereof.
 25. The method of claim 13, wherein saidproton conductive membrane comprises a ceramic material.
 26. The methodof claim 13, wherein electrical shocking is used to prevent electrodesurface fouling and particulate deposition on said electrodes.